Earth loader



y 9, 1964 A. c. ANDERSON 3, 33,553

EARTH 1.0mm Filed March as, 1962 2 Sheeiss=5hee 1 A 3/ 92 Y FIGJ. "f

3,133,653 EARTH LOADER Arthur (I. Anderson, Wildwood Crest, N.J., assignor to A. C. Anderson, In c., Wildwood, N.J., a corporation of New Jersey Filed Mar. 23, 1962, Ser. No. 182,016 6 Claims. (Cl. 214-140) The present invention relates to earth loaders and the like and is directed more particularly to bucket control means operable to prevent spillage of the contents of the bucket on the operator during raising of the bucket.

Earth loaders of the type to which the present invention relate generally include a tractor or the like, a pair of lift arms pivotally mounted to the tractor, a bucket, shovel, lift fork or the like pivotally supported between outer free ends of the lift arms and hydraulic actuator means to effect pivotal movement of the bucket relative to the lift arms. The lift arms are actuatable to move the bucketbetween a lower position to the front or rear of the tractor to scoop material into the bucket and an upper position above the tractor to facilitate dumping of the contents of the bucket into a vehicle for transport to another location.

A serious problem in loaders of this type is the danger of the bucket tilting toward the tractor during elevation of the lift arms and spilling the contents of the bucket on the operator and the tractor thereby jeopardizing the safety of the operator and possibly damaging the tractor. In some prior attempts to solve this problem, ,bucket leveling means, in the form of a parallel type linkage or the like is provided which is connected between the lift arms and the bucket. .The linkage effects a predetermined synchronized rotation of the bucket relative to the lift arms in a direction counter to the direction of pivotal movement of the lift arms during raising and lowering of the lift arms.

The major disadvantage of the linkage type leveling means is that since the pivotal movement of the bucket relative to the lift arms is predetermined and is the same for each cycle of the lift arms there is no assurance that the bucket is disposed in a truly level attitude under all operating conditions. For example, in a front end loader as illustrated in FIG. 1, if the tractor is inclined rearwardly, then the bucket as it is raised by the lift arms also inclines rearwardly toward the operator and there is the possibility of spillage of the contents on the tractor and operator. Accordingly in the operation of these loaders it is necessary forthe operator to observe the attitude of the bucket and manually control it to prevent spillage of the contents thereof. Furthermore linkages add to the cost of manufacturing the loader, are an additional maintenance factor, and are subject to damage thcreby'requiring replacement. Additionally, the linkages limit the range of maneuverability of the lift arms and the bucket.

Other attempts to solve the problem of bucket spillage include the provision of a hydraulic control system which serves the same function as the linkages, namely; to synchronize movement of the bucket and lift arms in a predetermined fixed manner during raising and lowering of the lift arms. The basic objection to the hydraulic system is the same as that regarding the linkages. There is no positive assurance against bucket spillage on the operator under all operating conditions. Where the loader is disposed on an incline, it is necessaryfor the operator to observe and control the bucket. Moreover these hydraulic systems are complicated, very expensive, and require precise design to correlate the hydraulic actuating assemblies for the lift arms and bucket.

In accordance with the present invention, bucket control means is provided operable to prevent the bucket from tilting from a truly level attitude toward the operator Patent I 3,133,653 Patented May 19, 1964 edge of the front and rear wall of the bucket is parallel to a horizontal reference plane. True bucket leveling is accomplished by providing valve means operatively connected to the hydraulic bucket actuator, means operable in one position to rotate the bucket in a directioncounter to the direction of rotation of the lift arms when the bucket tends to tilt from a truly level attitude toward the operator and sensing means on the bucket operable to. sense when the bucket begins to tilt from a truly level attitude toward the tractor and operable to actuate the valve to correct the tilting movement whereby spillage of the contents of the bucket during raising of the lift arms is precluded.

From the foregoing it may be seen that the present invention overcomes the major drawback of prior bucket controls by positively insuring against spillage during raising of the lift arms regardless of the disposition of the tractor. Moreover loaders embodying the bucket control means of the present invention are less expensive to manu facture and maintain than prior loaders employing parallel linkages or expensive hydraulic control circuits and invention is to provide novel bucket control means for earthloaders operable to prevent tilting of the bucket from a truly level attitude toward the operator to thereby eliminate the risk of spillage of the contents of the bucket on the operator regardless of the disposition of the loader.

Another object of the present invention is to provide an earth loader including bucket control means which is inexpensive to manufacture and maintain and is fully effective in operation and use.

These and other objects of the present invention and the various details of the operation and construction thereof are hereinafter more fully set forth with reference to the accompanying drawings, wherein:

FIG. 1 is a side elevational view of an earth loader embodying bucket control means in accordance withthe FIG. 3 shows a schematic hydraulic circuit'for another embodiment of bucket control means in accordance with the present invention; v

FIG. 4 is an electrical diagram showing schematically some of the elements of bucket control means in accordance with the present invention; and g FIG. 5 is an elevational view partially in section of the control valve of the bucket control means in its bucket leveling position. v

Referring now to the drawings, there is shown in FIG. 1 an earth loader embodying bucket control means in accordance with the present invention. The loader comprises a conventional tractor 1-0, an upstandingsupport member 11 disposed on each opposite side of the tractor 10, a lift arm 13 pivotally connected to each of the sup port members 11 and a bucket 14 pivotally supported a cylinder 20 pivotally mounted at 22 to the support frame and a piston rod 24 pivotally mounted at its outer free end to the elbow of the lift arm. Identical hydraulic actuators25, 2511 are provided for effecting pivotal movement of the bucket 14 with respect to the lift arms 13. The hydraulic actuator 25 comprises a cylinder 26 pivotally connected at 28 to the lift arm 13 and a piston rod 30 pivotally connected at its free end to the bucket 14. Raising and lowering of the lift arms and pivotal movement ofthe bucket 14 with respect to the lift arms .are controlled by means of a conventional 4-way reversing valve 32 including a lift arm control lever 34 and a bucket control lever 36 which as illustrated in FIG. 1, are conveniently disposed within the reach of the operator.

The hydraulic system for effecting selective actuation of the lift arms 13, and bucket 14 through the 4-way valve 32 is shown schematically in FIG. 2. The hydraulic system includes a conventional hydraulic pump P connected at its intake side to a sump S through a line 40 and at the delivery or pressure side .to the valve 32 through a line 42. The valve 32 is connected through a pair of lines 44 and 46 with the upper and lower ends respectively of the bucket control cylinders 26, 26a. The valve 32 is also connected through lines 48 and 50 to the upper and lower ends respectively of the lift arm control cylinders 20, 20a.

Considering now the operation of the loader, assume that the lift arms are disposed in the lower position with the bucket 14 directly in front of the tractor in position to scoop material, material may be scooped up by merely driving the tractor forwardly. After sufficent material has been received in the bucket 14, the operator may rotate the bucket 14 in a counterclockwise direction to prevent the material from dropping out by moving the bucket control lever 36 from the neutral position shown in FIG. 1 to the left toward the operator which through the valve 32 establishes fluid communication between lines 42 and 44 to permit flow of fluid under pressure from the pump P to the upper end' of each of the cylinders 26, 26a and opens line 46 to the sump S through the line 51 to permit flow of fluid from the lower end of each of the cylinders 26, 26a to the sump S. Accordingly, the piston rods 30, 30a are retracted into their respective cylinders thereby causing a counterclockwise pivotal movement of the bucket 14. When the bucket has been rotated to a desired position, the control lever 36 is moved to the neutral position. Thereafter if it is desired to raise the bucket 14 to the upper position shown in FIG. 1, the operator moves the lift arm control lever 34 from the neutral position shown in FIG. 1 to the left which admits fluid under pressure through the line 50 to the lower end of each of the cylinders 20, 20a and opens the return line 48 to the sump S through the line 48a, a valve 59, the line 48b, the valve 32 and the line 51. This causes the piston rods 24, 24a to be extended or moved outwardly of their respective cylinders 20, 20a thereby effecting a counterclockwise pivotal movement of the lift arms 13. Thereafter when it is desired to dump the contents of the bucket, the bucket control lever 36 is moved from its neutral position to the right with respect to FIG. 1 which through the valve 32 causes a reversal of fluid flow in the lines 44 and 46 from that described above to effect clockwise rotation of the bucket 14. After dumping the contents of the bucket 14, the lift arms 13, may be lowered from the position shown in FIG. 1 by moving the control lever 34 to the right with respect to FIG. 1 which reverses flow in the lines 48 and 50 to effect clockwise rotation of the lift arms .13 to lower the same.

In accordance with the present invention, bucket control means is provided operable to prevent the bucket from tilting toward the tractor from a truly level attitude during raising of the lift arms thereby insuring against spillage of the contents of the bucket on the operator and tractor. This is accomplished by providing a control valve 59 in the hydraulic circuit actuatable to a bucket leveling position in rscponse to sensing means, in the present instance a mercury switch 92 on the bucket which senses when the bucket begins to tilt toward the tractor from a truly level attitude. In the bucket leveling position, the control valve 59 operates to effect pivotal movement of the bucket 14 to counter the rotation thereof toward the tree .2. 7, 11.. fay prm'enting the bucket from tilting toward the tractor from a truly level attitude during raising of the lift arms. A truly level attitude of the bucket 14 is one wherein a plane AA through the upper edge of the front and rear walls of the bucket is parallel to a horizontal reference plane wherein the contents of the bucket are retained against spillage from the bucket. In the present instance the upper edge 31 of the side walls 33 of the bucket also lie in the plane AA and the mercury switch 92 is mounted on one of the side walls 33 of the bucket parallel with the upper edge 31 thereof.

In the hydraulic circuit shown in FIG. 2, the control valve 59 is disposed in the lines 48, 48a and 48b connecting the upper ends of the lift arm cylinders 20, 20a with the 4-way valve 32 and is operable in its normal position to provide the normal flow directly from the line 48a to the line 48b, and in the bucket leveling position to effect flow of fluid from the line 48a to the line 46 and from the line 44 to the line 48b to effect pivotal movement of the bucket in a direction away from the tractor. To

this end, the control valve 59 comprises a generally cy-- lindrical valve body 54, an axial bore 56 extending therethrough, a spool 58 mounted for axial movement in the bore 56, four axially spaced ports 60, 62, 64 and 66 which from the port 60 to the passageway 68 and a needle I valve 72 is provided in the port 66 for selectively controlling the flow of fluid therethrough. The spool 58 is of reduced cross section at axially spaced sections to provide a land 74 therebetween and lands 76 and 78 adjacent axial ends of the spool 58. The spool 58 is normally biased to the left with respect to FIG. 2 by means of a coil spring 80 wherein the land 74 is disposed between the ports 60 and 62 blocking fluid communication therebetween and permitting flow between the ports 60 and 64 and the land 78 blocks the port 66. This position of the control valve 59 is termed the normal operating position wherein the raising and lowering of the lift arms and pivotal movement of the bucket 14 relative to the lift arms may be controlled through the 4-way valve 32 by manipulation of the levers 34 and 36 in the manner noted above.

The spool 58 is actuatable to the position shown in FIG. 5, the bucket leveling position of the control valve 59, upon energization of a solenoid which through an electric circuit shown schematically in FIG. 4 energizes the solenoid 90 when the bucket starts to tilt toward the tractor from a truly level attitude during elevation of the lift arms. The circuit includes the mercury switch 92 which is connected in a series through a lead 93 with a mercury control switch 94 mounted adjacent the lift arm control lever 34 and through lead 96 with the coil 101 of a conventional relay 98. The mercury control switch 94 is normally open and is closed only when the lift arm control lever 34 is moved to the left to raise the lift arms thereby depressing a plunger to close the mercury control switch 94. The mercury control switch 94 is connected through a lead to a source of energy, for example a conventional battery 102 which in turn is connected through a lead 104 to the coil 101 of the relay 98. The battery 102 is also connected through a lead 106 to the normally open contacts 105 of the relay 98. The solenoid 90 is connected through a lead 110 to the contact 105 and through a lead 112 to the lead 100. By this arrangement the solenoid 90 is energized only when both the mercury switch 92 and the mercury control switch 94 are closed, the mercury control switch 94 is closed only when the lift arm control lever 34 is moved to the left with respect to FIG. 1 to raise the lift arms and the mercury switch 92 is closed only when the upper edges 31 of the side walls 33 of the-bucket 14 tend to tilt toward the tractor from a truly level attitude.

Considering the operation of the earth loader embodying bucket control means in accordance with the present invention, assume that the lift arms 13 are in the lower position with the bucket 14 in front of the tractor and that the bucket 14 has been rotated to a position wherein the open end thereof faces'upwardly to prevent the material from falling out of the bucket. Now; if the operator desires to raise the bucket'14 to facilitate dumping of the material into a transport vehicle, the lift arm control lever 34 is moved to the left with respect to FIG. 1.- Actuation of the lift arm control lever 34 depresses the plunger 95 to close the switch 94 and also permits flow of fluid under pressure from the line 42 through the valve 32 and line 50 to the lower ends of the lift arm 6 to the position shown in FIG. 2. control valve 59 remains in its normal operating position during lowering of the lift arms since the switch 94 remains open.

There is shown in FIG. 3 another embodiment of bucket control means in accordance. with the present invention operable to prevent tilting of the bucket toward 'the tractor f om truly level attitude during raising the lift arms. The basic elements of the hydraulic circuit include a 4-way valve 132, a pump P connected through a line 142 to the valve 132 and through a line 140 to a sump S. Lines 148 and 150 connect the valve 132 to the upper and lower ends respectively of the lift arm control cylinders 120, 120a and lines 144 and 146 connect the control valve 132 to the upper and lower ends of the bucket control cylinders 126, 126a. The lift arms 13 and bucket 14 are selectively actuatable through the valve 132 by manipulation of the bucket control lever 36 and the lift and a bucket leveling position. The structural details of l the control valve 159 may be identical to the valve 59 and cylinders 20, a thereby causing the piston rods 24, 24a

to be extended and rotate the lift arms in a counterclockwise direction. As illustrated in FIG. 2, the control valve 59 is in the normal operating position wherein the lines 4801 and 48b are in communication through the ports 60 and 64 and the lands 76 and 78 block the ports 62 and 64 respectively. Accordingly fluid from the upper end of the cylinders is free to flow through the lines 48a and 485, through the control valve 59 and main valve 32 to the sump S.

If during raising of the lift arms 13; the bucket 14 tends to tilt toward the tractor from a truly level attitude wherein thetop edge of the bucket 14 starts to incline toward the tractor with respect to a horizontal reference plane, the ball of mercury in the switch 92 moves to the left with respect to FIG. 4 to close the contacts whereby the relay coil 101 is energized which in turn energizes the solenoid 9t). Energization of the solenoid 90 moves the spool 58 to the position shown in FIG. 5, the bucket leveling position of the control valve 59. In this position of the spool 58, the ports 60 and 62 are in fluid communication permitting flow of fluid from the line 48a through the control valve 59 and line 82 to the lower ends of the bucket cylinders 26, 26a. Fluid from the upper end of the bucket control cylinders 26, 26a'is free to flow through lines 44, line 86, ports 66 and 64 to the sump S. This flow of fluid moves the piston rods 30, 30a outwardly of their respective cylinders 26, 26a to thereby rotate the bucket 14 clockwise with respect to the lift arms 13 to counter rotation of the bucket 14 by the lift arms and thereby prevent spillage of the contents of the bucket. It is noted that the needle valve 72 throttles flow of fluid from the upper ends of the bucket control cylinders 26, 26a and may be adjusted selectively to control the rate of flow through the port 65 to provide means for controlling rate of levelingof 'the bucket. It is noted further that the ball check '70 permits excess flow of fluid from the lift arm controlcylinders 20, 20p to pass through the passageway 68 to the sump S whereby the lift arm and bucket'control cylinders need not be designed with the same capacity. The control valve 59 remains in a t bucket leveling position to correct the attitude of the bucket as needed automatically and maintain it in a truly level attitude whereby the operator neednot be concerned with bucket spillage during raising of the lift arms 13.

the upper ends of the bucket control cylinders 126, 126a through the lines 144, 186, ports 166 and 164 to the lower include a valve body 154, an axial bore 156, a spool 158 mounted for axial movement in the bore 156 and a plurality of axially spaced radially extending ports'160, 162, 164 and 166. The spool 156 is of reduced cross section at axially spaced sections to define a land 179 therebetween and lands 176 and 178 at axial ends of the spool In accordance with this embodiment of the invention, 1

the control valve 159 is disposed between the lines. 144 and 146 and is actuatable in response to' the mercury switch 92 to a bucket leveling pdsition to counter rotation,

of the bucket toward the tractor from a truly level attitude during raising of the lift arms. To this end the ports 164 and 166 are connected through lines 182 and 186 to the lines 146 and 144 respectively and the ports and 162 are closed off by plugs. The spool 158 is normally biased by means of a coil spring to the left with respect to 7 FIG. 3, the normal operating position of the valve 159 and a solenoid 190 is provided which upon energization through an electric circuit identical to thatshown in FIG.

the bucket 14, the center of gravity of the bucket 14is disposed forwardly of its pivotal connection to the lift arms 13 whereby the weight of the bucket tends to rotate it away from the tractor in the present instance, in a clockwise direction. The operator may raisethe lift arms 13 and bucket 14 by moving the lift arm control lever 34 to the left with respect to FIG. 1 thereby depressing the plunger 95 to close the switch 94. If during raising of the lift arms, the bucket 14 starts to tilt toward the tractor from a truly level attitude, the mercury switch contacts are closed thereby energizing the solenoid 190 whereby the spool 158 is moved to the position shown in FIG. 5. In this position, the weight of the bucket on the piston rods of the cylinders 126 and 126a causes fluid to flow from end of the bucket control cylinders through the lines 182 and 146 thereby rotating the bucket in a clockwise direction and preventing it from tilting toward the operator from a truly level attitude. Fluid flow is in the direction indicated rather than in an opposite direction due to l the normal tendency of the bucket 14 to rotate in a clockwise direction. It is noted that the needle valve 172 meters flow of the fluid to thereby control the rate of It is noted that the' lcvc.ing and is adjustable selectively to increase or decrease the rate of fluid flow. Control of the attitude of the bucket 14 in this manner continues automatically as necessary during elevation of the lift arms. When the lift arms .13 have been raised to a desired height, the operator moves the lift arm control level 34 to the neutral position thereby opening the switch 94 which through the electrical circuit de-energizes the solenoid 190 whereby the spool 158 returns to the position shown in FIG. 3 and prevents flow between'the upper and lower ends of the bucket control cylinders 126, 1260.

From the foregoing it may be seen that the present invention provides novel means for controlling the attitude of the bucket during raising of the lift arms whereby tilting of the bucket from a truly level attitude toward the tractor is prevented thereby precluding spillage of the contents of the bucket on the operator or the tractor.

It is further apparent that the control means is comparatively simple and fully effective in operation and use.

While particular embodiments of the present invention have been illustrated and described herein, it is not intended to limit the invention and changes and modifications may be made therein within the scope of the following claims.

I claim:

1. In an earth loader or the like including a tractor, lift arm means pivotally connected at one end to said tractor, a bucket pivotally connected to the outer free end of said lift arm means, first hydraulic actuator means for effecting pivotal movement of said lift arm means between a first position wherein said bucket is disposed adjacent one end of said tractor and a second position wherein said bucket is disposed above said tractor, sec ond hydraulic actuator means for effecting pivotal movement of said bucket relative to said lift arm means, manually operable valve means for selectively effecting pivotal movement of said lift arm means and pivotal movement of said bucket relative to said lift arm means, fluid lines connecting said manually operable valve means to said first and second hydraulic actuator means, control means operable to prevent said bucket from tilting from a truly level attitude toward said tractor during pivotal movement of said lift arm means from said first to said second positions, comprising control valve means disposed in said fluid lines between said manually operable valve means and said hydraulic actuator means operable between a normal operating position wherein pivotal movement of said lift arm means and said bucket is controlled by said manually operable valve means and a bucket leveling position, sensing means on said bucket operable to sense when said bucket tends to tilt from said truly level attitude toward said tractor and operable to actuate said control valve means to said bucket leveling position to effect flow of fluid from said first hydraulic actuator means to said second hydraulic actuator means thereby to effect pivotal movement of said bucket counter to the direction of pivotal movement of said lift arm means whereby spillage of the contents of the bucket on the tractor during actuation of the lift arm means from said first to said second position is prevented.

2. In an earth loader as claimed in claim 1, wherein said control valve means includes an adjustable needle valve operable to throttle flow of fiuid through said control valve when in said bucket leveling position thereby providing means for controlling selectively the rate of bucket leveling.

3. In an earth loader as claimed in claim I wherein said control valve means includes a ball check operable to permit excess fluid flowing from said first hydraulic actuator means to bypass said second hydraulic actuator operable when energized to actuate said control valve to. said bucket lcveiing position and electric circuit means connecting said mercury switch to said solenoid, said mercury switch adapted to close when said bucket tends,

to tilt toward said tractor from said truly levcl= attitude whereby said solenoid is energized and said control valve f is actuated to said bucket leveling position.

5. In an earth loader as claimed in claim 4, wherein said electric circuit means includes a normally'open mercury control switch connected in series with said mer cury switch and adapted to close when said manually t operable valve means is actuated to effectpivotal move-.

ment of said lift arms from said first to said second posi-.

tions whereby said control valve means is actuatable to a. bucket leveling position only during pivotal movement of said lift arm means from said first to said' second posi-' tion and when said bucket tends to tilt toward-said tractor.

from a truly level attitude. 1-

6. An earth loader or the like comprisinga tractor,

lift arm means pivotally connected at one end to the tractor, a bucket pivotally connected to the outer free end of said lift arm means, the center of gravity ofv said bucket being disposed with respect to the pivotal connection of the bucket to said lift arm means whereby the weight of the bucket tends to rotate the bucketin a direc-l tion away from said tractor, means for pivoting said lift arm means between a first position wherein said bucket,

is disposed adjacent one end of said tractor and a-second position wherein said bucket is disposed above said tract-j g" tor, hydraulic actutaor means for effecting pivotal'move' ment of said bucket relative to said lift arm means in-" eluding at least one cylinder. pivotally connected to said.

lift arm means and a fiuid actuated piston rod mounted in said cylinder for movement axially therein and pivotally connected at its free end to said bucket, controfvalve' means operable to prevent said bucket from tilting from. a truly level attitude toward said tractor during pivotal movement of said lift arm means from said first to said second positions, a first fluid line connecting saidcontrol valve to one end of said cylinder, a second fluid lineconnecting said control valve to the opposite end of said cylv inder, said control valve operable in a bucket leveling position to permit flow of fluid from one end of saidcyiinder through said control valve to the opposite end of said cylinder thereby to actuate said piston rod axially of its cylinder to effect pivotal movement of saidv bucket counter to the direction of pivotal movement of said lift arm means to prevent said bucket from tilting from said truly level attitude toward said tractor and sensing means on said bucket operable to sense when said bucket tends to tilt from said truly level attitude toward said tractor and actuate said control valve to said bucket leveling position whereby spillage of the contents of the bucket on the tractor during actuation of the lift arm means from said first to said second positions is prevented. I

References Cited in the file of this patent v UNITED STATES PATENTS 1,907,639 Young May 9, 1933 2,765,808 Tydcman Oct. 9, 1956 2,876,921 Salna Mar. 10, 1959 2,946,144 Anderson July 26, 1960 2,988,891 Hemings June 29, 1961 

1. IN AN EARTH LOADER OR THE LIKE INCLUDING A TRACTOR, LIFT ARM MEANS PIVOTALLY CONNECTED AT ONE END TO SAID TRACTOR, A BUCKET PIVOTALLY CONNECTED TO THE OUTER FREE END OF SAID LIFT ARM MEANS, FIRST HYDRAULIC ACTUATOR MEANS FOR EFFECTING PIVOTAL MOVEMENT OF SAID LIFT ARM MEANS BETWEEN A FIRST POSITION WHEREIN SAID BUCKET IS DISPOSED ADJACENT ONE END OF SAID TRACTOR AND A SECOND POSITION WHEREIN SAID BUCKET IS DISPOSED ABOVE SAID TRACTOR, SECOND HYDRAULIC ACTUATOR MEANS FOR EFFECTING PIVOTAL MOVEMENT OF SAID BUCKET RELATIVE TO SAID LIFT ARM MEANS, MANUALLY OPERABLE VALVE MEANS FOR SELECTIVELY EFFECTING PIVOTAL MOVEMENT OF SAID LIFT ARM MEANS AND PIVOTAL MOVEMENT OF SAID BUCKET RELATIVE TO SAID LIFT ARM MEANS, FLUID LINES CONNECTING SAID MANUALLY OPERABLE VALVE MEANS TO SAID FIRST AND SECOND HYDRAULIC ACTUATOR MEANS, CONTROL MEANS OPERABLE TO PREVENT SAID BUCKET FROM TILTING FROM A TRULY LEVEL ATTITUDE TOWARD SAID TRACTOR DURING PIVOTAL MOVEMENT OF SAID LIFT ARM MEANS FROM SAID FIRST TO SAID SECOND POSITIONS, COMPRISING CONTROL VALVE MEANS DISPOSED IN SAID FLUID LINES BETWEEN SAID MANUALLY OPERABLE 